Getter for electron tubes



Aug. 30, 1960 J. LE FERSON CETTER FOR ELECTRON TUBES Filed Dec. 4, 1958 IIIIIIIII Ill VA/I

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INVENTOR.

JOSEPH LEFERSON AGENT Uite oarrna FoR ELECTRON TUBES Filed Dec. 4, 1958, Ser. No. 778,154

4 Claims. (til. 313178) This invention relates to improved getters for electron tubes and has particular reference to rigidified electrode structures which employ platinum, and to getters for use therewith, and method of making same.

In the manufacture of high power electron tubes, grids are sometimes conveniently made at least in part of platinum-clad molybdenum wire which has been found to provide the grids with more desirable operating characteristics. For gettering various gases in such tubes, zirconium is a highly desirable material. Before the use in grids of platinum-clad molybdenum wire, zirconium was sprayed on the grid supporting structure and then sintered at a temperature of about 1250-1400" C.

However, when platinum-clad grids were provided in this manner with getters it was found that the grid became less eflicient and in some cases the tubes were damaged. I found that these undesirable factors were caused by sintering the zirconium at relatively high temperatures which the platinum cladding could not withstand. Lowering the sintering temperatures resulted in poor sintering whereupon the zirconium easily separated from the grid stays. This caused the existence of loose particles in the tube. In some cases oxidized zirconium, which does not possess the desired gettering characteristics, resulted from the lower sintering temperatures.

I found that a zirconium getter may be combined with a platinum-clad grid structure by separately spraying the zirconium on individual strips of metal, sintering the sprayed strips, and then assembling the sintered strips in channel-shaped grid stays whereupon the strips will not only satisfactorily perform the gettering operation but will also rigidity the delicate grid structure. Such grid structures are able to withstand the temperatures used in normal vacuum outgassing processes, during which processes the zirconium functions to efiiciently remove various gases emanating from the structures.

Accordingly, it is a primary object of this invention to provide a sintered zirconium getter in an electron tube employing a platinum-clad g'n'd.

Another object is to provide a getter of the above character which may be used to reinforce and rigidity the grid structure.

Another object is to provide a getter of the above character which may be made to extend throughout areas of different temperatures within the tube so that it may efliciently getter various gases which are known to getter at different temperatures.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawing wherein:

Fig. 1 is a front elevational view of a grid structure embodying the invention;

Fig. 2 is a horizontal sectional view of the grid structure taken substantially on line 22 of Fig. 1, and

Fig. 3 is an enlarged horizontal sectional view through -a grid stay taken on line 3-3 of Fig. 1.

Referring more particularly to the drawing, the grid structure embodying the invention comprises four paratent allel spaced channel-shaped upright supports or stays 10, 11, 12 and 13 which are secured at the ends to suitable caps 14 and 15 which maintain the stays in parallel positions relative to one another. The stays are arranged in a generally circular configuration, as shown in Fig. 2, with their open sides preferably directed outwardly.

Over the stays is wound a spiral wire 16 which forms the active grid element, wire 16 being preferably molybdenum having a coating of platinum thereon. The platinum-clad wire 16 is spirally Wound throughout substantially the full length of the stays 1013 and the respective turns or windings are spaced apart a required distance so that electrons will pass through the structure in the normal operation of electron tubes.

It is necessary during the manufacturing process of electron tubes, as well as during subsequent operation, to remove from the interior of the tube occluded gases which may be detrimental to tube operation. This is done by means of a gettering material such as zirconium, titanium, tantalum or the like which is placed within the tube where it will function, when heated, to remove such gases.

Various gases are known to getter at various different temperatures. Therefore, it is advisable to place the getter in different portions of the tube which have different operating temperatures. In order to accomplish this, I have found that zirconium or other selected getter material can be applied to the grid stays for a substantial portion of their lengths, and since various portions of the grid lie in diiferent temperature zones, these getters will efliciently getter the various gases.

Sprayed coatings of zirconium which are sintered onto the grid stays are eflicient getters when used with conventional grid structures. However, platinurn-clad grid wires cannot withstand the heat required to sinter the getter onto the stays. Sintering is best performed at a temperature of about 12504400 C. However, at such temperatures, the bond between the platinum and molybdenum is destroyed, allowing the platinum to vaporize or fiow, producing a poorly operating grid.

Reducing the sintering temperature to a level where the platinum-molybdenum bond is not damaged results in poor sintering or in the production of oxidized zirconium.

Therefore, in accordance with this invention, I have founnd that satisfactory getters can be provided by spraying a thin layer 17 (Fig. 3) of zirconuim onto separate and individual strips 18 of molybdenum or other selected metal, sintering the sprayed strips, and subsequently mounting the strips 18 in the respective channels of stays 1013. The strips may be held in place by spot welding, riveting or other suitable means.

Thus, by sintering the sprayed zirconium 17 on the strips 18 prior to assembling the strips with the grid structure, no damage is done to the platinum cladding on the wires 16.

The strips 18 are preferably but not necessarily made of a width closely approximating the width of the channels in the grid stays 10-13. When assembled, the strips reinforce the stays and increase the rigidity of the entire grid structure. The strips also are made to extend nearly the entire lengths of the stays so that various portions thereof are disposed in different temperature zones. In this way more efficient gettering is achieved.

From the foregoing it will be seen that I have provided an improved getter for electron tubes embodying elements having platinum cladding thereon, which getter not only functions to efficiently getter various gases within the tube but also reinforces and rigidizes the structure on which it is mounted.

It is to be understood that various modifications of this invention may be made by those skilled in the art without departing from the spirit of the invention as exemplified and defined by the accompanying claims.

Iclairn;

1. In an electron tube having a generally cylindrical gridst'ructure employing a spirally Wound grid wire having a platinum surface, supporting means for the grid Wire comprising a number of elongated stays extending longitudinally of the grid and over which the grid wire is wound, the stays each being channel-shaped with the channels extending longitudinally in one side of the stays, and getter means comprising a strip of getter material located in the channel of at least one of said stays and extending for a substantial distance of the length thereof, the strip being fixedly secured to the stay within the channel and having a layer of gettering material sintered to a surface thereof.

2. A device substantially as set forth in claim 1 References Cited in the file of this patent UNITED STATES PATENTS 1,892,819 Gessel Jan. 3, 1933 1,949,849 Gessel Mar. 6, 1934 2,362,468 Clark Nov. 14, 1944 2,418,390 Atlee Apr. 1, 1947 2,741,717 Katz Apr. 10, 1956 

